It is known in the art (British No. 777,087) that cyclohexyl hydroperoxide (CHHP) is formed in the air oxidation of cyclohexane (cyane) along with cyclohexanone and cyclohexanol. It is also well recognized that cyclohexanone and cyclohexanol can be converted by oxidation to adipic acid and that CHHP can be converted to cyclohexanone (K) or cyclohexanol (A) either in the course of the cyane oxidation or in a separate decomposition or conversion step.
The development of processes for providing an optimum yield of adipic acid from these several intermediates has been the subject of extensive effort. Because CHHP may be used as an oxidizing agent for various purposes such as the oxidation of olefin materials, as well as an intermediate to the adipic acid precursors, K and A, cyane oxidation processes have been sought which would give a high proportion of CHHP in the reaction product.
In U.S. Pat. No. 2,851,496 there is described a process for oxidizing cyane with or without a catalyst to give the corresponding hydroperoxide (CHHP) along with the adipic acid precursors K and A, and thereafter converting or decomposing the CHHP into K and A by heating in the presence of a decomposition catalyst.
In U.S. Pat. No. 3,530,185 there is described a multistep process wherein cyane with or without catalyst is oxidized to give primarily K and A with lesser amounts of CHHP. In general, as stated in U.S. Pat. No. 3,530,185 and noted also in Japanese publication Oxidation, published by Kagaku Kogyo Sha, Aug. 10, 1963, pages 144-146, if catalyst is present the CHHP tends to be decomposed and the main products are K and A.
It is further known that in the air oxidation of cyane in the absence of a catalyst a high proportion of the oxidized products is in the form of CHHP. In U.S. Pat. No. 3,510,526 a process is described which gives high yields of hydroperoxide by the air oxidation of a cycloalkyl compound such as cyane in the absence of a catalyst, in apparatus previously rendered passive by treatment with sodium pyrophosphate to minimize any catalytic effects of the equipment and with the added step on treating recycled cycloalkane with base to remove acidic by-products. Obtaining an increased yield of hydroperoxide by carrying out the oxidation in presence of an aqueous solution of an alkali metal or calcium pyrophosphate has also been described (U.S. Pat. No. 2,798,096).
As noted above, air oxidation of cyane gives rise to the adipic acid precursors K and A as well as CHHP, which in turn can be converted to K and A. A complication attending the use of the various processes described is that appreciable amounts of peroxides other than CHHP may also be formed in the air oxidation of cyane and these also can undergo decomposition or conversion but to products other than K and A. This is indicated to be the case in U.S. Pat. No. 2,851,496, in U.S. Pat. No. 3,530,185 and in U.S. Pat. No. 3,719,706, the latter of which describes a process for isolating and utilizing a peroxide other than CHHP, namely 6-hydroperoxyhexanoic acid.
Accordingly, a process has been sought for air oxidation of cyane which would provide a product stream containing a high proportion of CHHP along with K and A and which would be substantially free of peroxides other than CHHP.